Many different methods and types of equipment are known for reducing pollutants in the treatment of waste water. Some of these known methods and apparatus are specially designed for use in relatively confined tanks (or wet wells scum pits etc.) In U.S. Pat. Nos. 4,670,149 (Francis) and 4,680,111 (Ueda), bacterial incubators are floated or suspended near or just below the surface of the water being treated; and the Francis patent provides for the augmentation of the processes for decomposing organic waste by the addition of highly-cultivated strains of microorganisms having a high capacity for "specific organic reduction of grease and other troublesome substances".
The just-described bacterial incubator beds are filled with a plurality of one or more types of well-known bio-suspension elements which are usually made from injection molded resins and specially designed to provide large surfaces conducive to the growth of bacterial colonies, while at the same time providing excellent liquid flow through and around the surfaces to disperse the bacteria in a controlled fashion in the liquid phase. One such well-known bio-suspension element has an overall spherical shape, is approximately 2 inches (5 cm) in diameter, and has an open construction formed by a multiplicity of circular members which join and support a plurality of internal cross members.
Aeration devices which create very fine bubbles of air are also particularly suited to the treatment of wastes in relatively confined bodies of water. Examples of the latter are disclosed in U.S. Pat. Nos. 3,490,752 (Danjes et al.); 3,664,647 (Snow); and 4,215,082 (Danel).
Other known prior art devices are specially designed for use in larger bodies of water, e.g., ponds, lagoons, etc.; and all of these are directed to the aeration of the water by agitation, using such means as paddle-wheels, pumps, and water jets. For example, a large mixing pump is shown in U.S. Pat. No. 4,072,612 (Daniel), while water-jet mixers are disclosed in U.S. Pat. No. 3,984,323 (Evens) and French Patent No. 1.377.571. Some of these agitators are specially designed to float on the surface of the water: a floating paddle-wheel agitator is shown in U.S. Pat. No. 3,589,997 (Grutsch et al.), while U.S. Pat. No. 4,191,479 (Shuck et al.) shows a floating paddle-wheel agitator combined with an air compressor and an air distribution pipe that can be lowered into the pond as deep as 10 feet to deliver high-velocity air to disrupt and agitate the sludge. A floating centrifugal pump is disclosed in U.S. Pat. No. 4,086,306 (Yoshinaga).
A floating unit disclosed in U.S. Pat. No. 4,350,589 (Stog) provides water-jet aeration in combination with air-bubble confinement means causing the bubbles to remain longer in contact with the microorganisms present in the water being treated. Finally, South African Patent No. 358 414 (Stog) shows floating apparatus similar to the previously-described Stog unit in which microorganisms developed within the unit are collected from the downstream path and recycled, being reintroduced in or behind the water-jet aeration/agitation pump along with new microorganisms. The floating unit of the latter reference utilizes plastic strings within its air-bubble confinement chamber for providing surfaces for the growth of the microorganisms.
The above-described prior art water treatment methods and devices are either inappropriate for use in relatively open bodies of water such as ponds and lagoons, or they suffer from serious deficiencies that make them less than satisfactory for such use, particularly where the water being treated is at near-freezing temperatures.